The invention concerns a vessel filter that includes a conductor loop that forms the inductance of an electrical resonance circuit.
Vessel filters are structures that are inserted into traversed veins and arteries of the human or animal body, especially the inferior vena cava, in order to prevent penetration of blood clots or sclerotic vascular material into organs of the body, especially the lungs and brain.
For application, vessel filters are generally mounted or fastened in the unexpanded state on a wire to be introduced to the body or brought to the target location of implantation in a catheter via a surgical vein access and then deployed. The diameter of the vessel filter is then enlarged, so that the filter presses against the vessel wall and is fastened there.
There is a requirement, for displaying of vessel filters by imaging methods during implantation and for later functional control or removal. Recently, magnetic resonance (MR) imaging systems have increasingly gained importance in medical diagnosis. Interventional and minimally invasive techniques, like puncture, catheterization and surgical procedures, in particular, are conducted under MR tomographic control. Depiction and position determination of a vessel filter in an MR imaging system, however, is difficult. Metal vessel filters are only visible as an artifact, and vessel filters made of plastic are scarcely visible at all because of their fine structure in the MR image.
It is known from WO-A1 99/19739 for a clear and signal-intensive representation of a medical device in an MR image to integrate in this device an oscillating circuit that generates an altered signal response in a locally limited region or around the medical device, which is depicted with location resolution. The resonance frequency of the oscillating circuit is essentially equal to the resonance frequency of the emitted high-frequency radiation of the MR imaging system. The to oscillating circuit in the medical device can then be made of the same material. In one variant, the oscillating circuit is integrated in the medical device, so that the inductance appears together with it during deployment of the device.
MR-active vessel filters are also known from the literature. These instruments consist of a filter part and a separate conductor loop wound around the filter. After introduction into the body, the conductor loop and vessel filter can be deployed.
A shortcoming in vessel filters of this type is the fact that they consist of a basic framework for the filter function onto which a conductor loop must be wound in order to provide the device with the desired MR activity. The connection of two components has an adverse effect on the mechanical stability of the vessel filter.
The task of the present invention is to provide a vessel filter characterized by good mechanical properties, especially a high degree of flexibility with simultaneous stability, and one that is readily viewable in an MR imaging system.
This task is accomplished according to the invention by a vessel filter with the features of a conductor loop, forming the inductance of an electrical resonance circuit. Preferred and advantageous embodiments of the invention are mentioned in the dependent claims. The conductor loop forms the vessel filter or at least parts of the vessel filter. The concept according to the invention therefore lies in using only one structure, namely, a conductor loop, both to form the actual filter and for the inductance. In combination with a capacitance, a resonance circuit is therefore provided.
In a preferred embodiment, the vessel filter forms several resonance circuits, each with at least one conductor loop. Because of this, a situation can be achieved in which the vessel filter can be operated and detected at several different MR frequencies. It can also be prescribed that several resonance circuits be coupled to each other.
In an advantageous variant, the vessel filter forms at least one integrated circuit coupled to the resonance circuits so that they can be adjusted or tuned by the integrated circuit in addition to the resonance circuit or the resonance circuits. The integrated circuit permits external influencing of the resonance frequency with to adjustment or tuning, for example, by switching on and/or switching off the inductive or capacitive elements of the oscillating circuit. The power supply of the integrated oscillating circuit can occur through a small power supply (for example, battery), or also by inductive coupling of energy from an electromagnetic field.
In an advantageous variant, the vessel filter has spacers and/or insulators that keep the individual sections of the conductor loops at a spacing from each other and/or insulate them relative to each other. Because of this, short circuits between individual conductor windings are prevented. In addition, the insulators, in a particularly advantageous variant, are simultaneously a part of the internal capacitance in conjunction with at least one conductor loop. This develops by a connection and simultaneous insulation of the ends with an insulator (for example, polymer, ceramic, composite) that represents a dielectric and forms at least one capacitance (capacitor) connected electrically in the network with at least two conductors separated by the insulator.
The conductor loop is advantageously enclosed by a nonconductor, especially plastic and/or ceramic. This serves for increased the lifetime of the vessel filter by increased mechanical stability and its disturbance-free function. In a particularly preferred variant, insulation serves to reduce and regulate the parasitic capacitance, wherein the insulation can also be used to tune the oscillating circuit, i.e., for fine adjustment of the resonance frequency. Fine adjustment is also possible by deformation of the filter and therefore a change in inductance. This can be determined primarily by expansion or compression or by limiting vessel diameter. The vessel filter according to the invention therefore gets by in its simplest variant without an additional capacitance, since a combination of an internal and parasitic capacitance is sufficient for its function. Insulation also ensures that no electrical contact to other conductor loops is present between the ends of the individual conductor loops which would alter the prescribed inductance by a short circuit.
In an advantageous variant of the vessel filter according to the invention, the resonance circuit has a resonance frequency, especially in the high-frequency range, which corresponds to the frequency of an external magnetic field, especially an MR tomograph (MRT). Implantation and function of the vessel filter can therefore be observed by imaging MR methods. However, it is also conceivable to provide an to oscillating circuit with a resonance frequency in a different frequency range.
In an advantageous variant, the conductor loop has at least one electrically nonconducting material on whose surface at least one conducting material is applied, especially gold, platinum, tantalum and/or conducting alloys. The choice of specially conducting materials, for example, gold, improves the formation of resonance. Several layers of an insulator and conductor can also be applied to the conductor loop.
The conductor loop of the vessel filter is advantageously designed so that it can be deployed. The resonance circuit can preferably be formed during and/or after implantation in a biological medium. The vessel filter can therefore be implanted in folded form and deployed during implantation or only at its target location. This permits implantation starting from small veins or arteries in the periphery of the body. However, in principle, it is also possible to form it before transplantation.
In an advantageous variant, the vessel filter according to the invention has several conductor loops. This permits greater flexibility in configuring the vessel filter and a higher filter function. In addition, the resonance can be further improved by the presence of several conductor loops.
“Conductor loop” is understood to mean a conductor consisting of one piece. “Conductor loop winding” is understood to mean a section of the conductor loop that is brought into a specific shape, in which the straight shape is also included.
In another advantageous variant, the so-called umbrella filter, the vessel filter has several conductor loop windings guided so that the conductor loop forms an elongated base that is closed on at least one side with a screen-like filter cage. This variant leads to a particularly good filter effect.
The term “filter cage” is used to denote the part of the vessel filter that contains the conductor loop windings, which, owing to the fact that they are brought together on at least one long side of the filter, are in a position to retain thrombi of clotted blood or sclerotic material in the blood vessel.
In another advantageous variant, the so-called diamond filter, the vessel filter has several conductor loop windings guided so that the largest spacing of the loop windings from each other is present in the center and tapers to at least one long side. In a particularly advantageous variant, the conductor loop windings taper to two sides, which improves the filter effect. Independently of the number of filter cages, the advantage of this variant lies in the fact that a large part of the conductor loop windings lies against the vessel wall, which leads to good and permanent and tilting-free fastening to the vessel wall, which can additionally be supported by anchoring in the vessel wall with hooks. In addition, this type of filter permits good illumination of the filter interior in the MR method.
In another advantageous variant, also referred to as a tulip filter, the vessel filter has at least one conductor loop winding that runs together in a filter cage on one side of the filter and extends leg-like on the other side of the filter. A filter forming at least one extension that serves for connection of the filter to a vessel wall is particularly preferred. With particular advantage, the regions of the conductor loop winding adjacent to the extension are at a limited spacing from each other. It is particularly preferred that the adjacent regions of the conductor loop winding in the extension be connected to each other without an intermediate space, especially by welding, soldering or pressing. However, they can also consist of one piece, i.e., the continuation is formed by a one-piece part connected to the conductor loop winding. Because of this, the contact surface of the vessel filter with the vessel wall is minimized and a situation is achieved in which the filter can be removed without rupturing the vessel wall, since the intima grows pocket-like around the extension.
It is particularly advantageous if the extension points in the direction of blood flow of the vessel in which the filter is arranged. Because of this, anchoring in the vessel wall and intima of the vessel is achieved, which optimally counteracts the flow force of the blood. To remove the vessel filter, the filter is initially moved against the direction of blood flow, in order to remove the extension from the intima pockets. After collapse of the filter, it can be removed without problem from the body.
It is also advantageous if the extension points in the direction of the vessel wall. This also requires a fixed anchoring in the vessel wall, both by growing of the intima around the extension and by concentration of the pressure force on this extension. Anchoring can be improved by additional hooks. An improved anchoring can be improved by a sealing coating with greater depth of roughness.
It is particularly preferred that the extensions be arranged moveably against the braces, for example, of the tulip filter. The resonance frequency of the filter also depends on its diameter. During deployment of this variant of the vessel filter, the extensions shift relative to the braces as a function of the vessel diameter, which determines the width of deployment. Because of the moveability, any change in resonance frequency is compensated by a change in filter diameter so that the resonance frequency remains almost constant as a result. Imaging in MR therefore remains optimally independent of vein diameter. Anchoring in this case is assumed by the fixed brace and is possible by anchoring with hooks.
In another advantageous variant, the so-called low-pass birdcage filter, the vessel filter contains at least two foldable conductor loops, especially guided in zigzag fashion, in which one conductor loop forms a capacitance at least one reversal point with at least another conductor loop or permits connection of an external capacitance, and the reversal points of at least one of the conductor loops on one side have a smaller spacing relative to each other than on the other side, and, in particular, form a filter cage.
In another advantageous variant, the so-called high-pass birdcage filter, the vessel filter contains at least two conductor loops guided in closed vessel filters in the longitudinal direction and connected on at least one end to another conductor loop by a capacitance.
Anchoring of the birdcage filter in the vessel wall can be produced by hooks. One means of connection for coupling between filters and catheters can also be a filter component.
In both cases, a very homogeneous magnetic field is created by the arrangement of inductances and capacitances according to the principle of a birdcage coil, which permits excellent. MR illumination and therefore intravascular imaging even of the immediate vicinity of the filter.
The design of a double-filter is particularly advantageous. This is understood to mean a vessel filter that forms a filter cage on both opposite long sides. Double-filters can be implemented, for example, in the variants of the umbrella, diamond and birdcage filter. The advantage of a double-filter lies in better illumination in the MR image with simultaneously optimized filter effect.
The individual windings of the conductor loops are advantageously arranged in the longitudinal direction of the vessel filter. This leads to a particularly mechanically to stable filter and also leads to good and permanent connection with the vessel wall. This is necessary, in particular, for a vessel filter permanently remaining in the vessel.
In an advantageous variant, the vessel filter according to the invention has at least one brace connected to the conductor loop. These braces improve the mechanical stability of the filter and increase the filter effect. At the same time, they can also serve to anchor it in the vessel wall. The braces can be fastened on their ends with plastic sealant or a crimping sleeve mounted in insulated fashion.
In another advantageous variant, the braces are conducting and are connected conducting to the conductor loop. Because of this, during use of conductor loop material, production is possible from only one piece. They therefore become part of the coil and can improve the resonance.
In a particularly preferred variant, the individual braces are connected moveably to the individual conductor loop windings.
A vessel filter containing braces made of bioresorbable material is particularly advantageous. After the braces are broken down by the body, the vessel filter has fewer connections to the veins or arteries than right before implantation. The vessel filter therefore sits loosely against the tissue. This permits easy removal of the implant from the body.
In an advantageous variant, the vessel filter forms at least one semiconductor element, especially a diode and/or a transistor and/or an integrated circuit. This diode permits tuning of the resonance frequency which leads to better detectability in an MR system. The transistor can also tune the oscillating circuit and be controlled via an additional inductive switching coil.
The conductor loop is advantageously formed from a material piece, especially a tube, a wire or electrically-conducting plastic. This permits simple and cost-effective production.
It is advantageous to produce the conductor loop by repeated lengthwise cutting of a tube, especially a Nitinol tube, and then expansion. It is particularly advantageous to guide the conductor loop on the sides in meander-like fashion. With this type of production, insulation of the conductor parts from each other is particularly facilitated.
The ends of the conductor loop windings are preferably joined by welding, gluing, clamping, sealing and/or shape-mating, especially by thermally initiated shrinkage of a cylinder from a shape-memory material.
In another advantageous variant, the vessel filter contains at least one conductor loop winding, provided with at least one hook. These hooks permit additional fastening of the filter in the vessel wall and therefore prevent filter wandering.
The vessel filter advantageously has at least one connection device, for example, a lug, for coupling with a device for introduction and/or extraction of the filter, for example, a catheter. This permits the operator's easy handling of the vessel filter during implantation and/or extraction.
The vessel filter also preferably contains at least one means for braking of the filter during introduction to the body. The braking device is preferably formed by a region of increased diameter or by a local constriction of the catheter. This permits the operator greater manual control and therefore more precise implantation in the blood vessel.
It is particularly advantageous, if the connection device is the braking device.